Probably aersolized blood/body fluids that were inhaled
Just a guess......
It certainly emphasizes the difficulty of isolating the patient. The smallest contact with even an incredibly small amount of virus containing fluid and you’re finished.
A Freep article on 4/16/14 discusses coughing and the size of dropplets remaining suspended in the air :
"In the cloud: How coughs and sneezes float farther than you think"
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Concur. In any evaporation process a small amount of the base fluid will be carried over. The virus will exist within that small amount of fluid. If the description of conditions is accurate, the air in that place has plenty of virus in it. The “protective clothing” I have seen in news photos would be completely ineffective in that environment.